Reorder libm LIBBUILTIN definition groups

The groups of libm LIBBUILTIN definitions are reordered to match the order of
the corresponding __builtin_* definitions (which occur earlier in the
Builtins.def file).

No functionality change intended.
ObjectiveC migrator: When inferring a property,
preserve getter's attribute. Also, do not attach
an inferred NS_RETURNS_INNER_POINTER to the inferred
property (it is illegal).